a) Field of the Invention
This invention relates to hypodermic needle/syringe assemblies and to a device for removing needles therefrom. It is more particularly concerned with needle/syringe assemblies used for injection of anesthetics in dental practice but it also has applicability in other fields of human and veterinary medicine.
b) Description of the Related Art
There is increasing concern about the dangers of infection arising from the use of hypodermic needles, particularly because of the health risks associated with diseases such as AIDS and Hepatitis B. Various devices have been proposed for the disposal of used needles. WO 88/06133 Bruno acknowledges a number of prior art disposal devices including one sold under the name "SHARPS--tainer" in the USA which comprises a jar-like container with a snap-on lid to which is mounted a plier-like device for grasping a needle hub and unscrewing it from the syringe. Bruno describes a needle removal and storage device which includes a manually-squeezable grasping device having opposed jaw-like segments to grasp the needle hub. CA 1,184,547 Frontier Plastics (South Wales) Limited describes a disposal bin having a top wall provided with a keyhole slot in which the needle can be engaged for removal from the syringe. EP 0,261,513 Bauer describes a similar device having a dumb-bell shaped slot in its top cover. Other removal devices are shown in GB 2,205,043A Jones et. al., GB 2,215,215A Snow Brand Milk Products Limited and EP 0,309,965A2 Nissho Corporation.
There is a known needle safety device which is illustrated in "Dental Update", March 1989, page 63. This device comprises a tapering sleeve having a hexagonal internal surface, and a broad hexagonal flange extending radially from the wider end of the sleeve and acting as a needle guard. When an operator is preparing to use a needle, he/she inserts the needle sheath into the sleeve of the safety device so that it becomes engaged therein. After the needle has been used, the operator can hold the device by the broad flange and reinsert the needle back into the sheath. By gripping the flange, the operator can then unscrew the needle/sheath assembly from the syringe. Subsequently the operator can press against the closed end of the sheath to make the needle/sheath assembly slide out of the safety device and fall into a disposal bin. However there is still a risk of needle-stick injuries with this device, particularly when the needle is being re-inserted into the sheath.
Another known device called "ON-GARD Recapper" sold by ON-GARD Systems Inc of Denver, Colo., U.S.A. comprises a broad flange at one end of a sleeve which incorporates a manually-operable gripping mechanism. When an actuator or the sleeve is depressed, a needle sheath can be inserted into the sleeve. The actuator is then released and the sheath is held by the gripping mechanism. The device is used in a manner similar to that described in the preceding paragraph, the actuator being released finally to transfer the used needle/sheath assembly to a disposal bin.
A further known device called "DisposiNeedle from Septodont" marketed by Deproco U.K. Limited, Maidstone, Kent, England comprises a needle guard, an oval sleeve incorporating a trigger mechanism, and a "sharps" container. After a needle/sheath combination has been screwed into the end of a dental syringe by hand, the sheath is inserted through the needle guard into the sleeve, the trigger mechanism being squeezed to permit entry of the sheath. The trigger mechanism is then released to grip the sheath. After use of the needle and syringe, the needle is replaced into the sheath. The dentist then unscrews the syringe from the needle with one hand while holding the "DisposiNeedle" device in the other hand. After the syringe has been disengaged, the trigger mechanism is activated again to allow the needle/sheath assembly to drop into the "sharps" container. Alternatively, the "DisposiNeedle" device can be used to remove a needle from a syringe without any sheath present.
U.S. Pat. No. 4,798,587 Willoughby describes a device comprising releasable gripping means for releasably gripping the needle and a drive mechanism for rotating the needle when gripped by the gripping means, the gripping means being designed so that the needle can move freely away from the gripping mechanism when released. The drive mechanism may be electric driven or manually operable. The releasable gripping means includes a pivotable lever for bringing one or more wheels and/or a rack into engagement with the needle hub in order to rotate it, and then for disengaging from the needle so that it can fall into a container.
Conventional hypodermic needles comprise a cannula having front and rear points, and a hub secured to the cannula. The hub generally has a body with a gripping surface which may suitably be octagonal or other non-cylindrical shape, and an annular shoulder which is of greater diameter than the gripping surface and which is located rearwardly of the gripping surface, i.e. nearer to the rear point of the cannula. This means that if the needle/syringe assembly is inserted into a gripping device such as a keyhole slot with the front point of the cannula pointing downwardly, and the syringe is then removed, the shoulder on the hub prevents the needle from falling into the container below, unless the needle is moved, which involves a risk of contaminating contact. Likewise with squeezable gripping means of the type described by Bruno or Willoughby or as in the "ON-GARD Recapper" and "DisposiNeedle" devices, it is necessary to move the gripping means apart before the needle can fall down into the container. As a result the needle comes into contact with movable or mechanical parts of the device, which may become contaminated and will be difficult to clean and sterilize.
There is an additional risk of disease being spread through the use of conventional syringes. Such syringes, particularly as used in dental practice, generally have a closed cap portion at each end, the rear cap having a hole for passage of the plunger, and the front cap having a hole for entry of the inner end of the cannula. A cartridge of anesthetic is inserted through a long slot in the barrel of the syringe and the rear point of the cannula pierces a rubber diaphragm at the front end of the cartridge. The hole at the front end of the syringe is generally of small diameter and there is a risk that the wall defining the hole may be contaminated as the rear point of one needle is withdrawn through it and thus contamination may be transferred to a fresh needle as it is being inserted into the syringe.
Contamination of the rear point of the needle may arise from body fluids such as blood being sucked up the needle, particularly in the course of "aspiration". Aspiration is a test carried out, particularly in dental practice, in order to ascertain whether the outer point of the needle has been inserted into a blood vessel. Gentle pressure is applied to the anesthetic in the cartridge and then this pressure is released; if the needle has been inserted into a blood vessel, blood will be sucked up the needle into the cartridge and will be visible there. When the needle is subsequently withdrawn from the cartridge after use, the exterior of the rubber diaphragm at the base of the cartridge may also become contaminated. This means that there is a potential health risk in handling the cartridges after use. Conventionally, cartridges are withdrawn through the slot in the syringe wall and disposed of separately from the needles.
GB 1,383,905 Amalgamated Dental Co. Ltd. describes a needle/cartridge/syringe assembly in which the syringe barrel is open at its front end but is internally screw-threaded while the hub of the needle has a skirt which can be introduced into the lower end of the barrel and engaged therein in screw-threaded relationship. The cartridge can pass in and out through the front end of the barrel. In use, the needle is assembled into the cartridge before the latter is inserted into the barrel of the syringe. After administering the injection, the needle and cartridge are removed from the syringe as one unit. No device for removing the needle/cartridge assembly is described. The needle hub as shown in the drawings of this specification also has a shoulder rearwardly of its gripping surface which would prevent the needle/cartridge assembly from falling into the container of a disposal device as described above. So far as the present Applicants are aware, the assembly of GB 1,383,905 has not been commercialized.
A known form of dental syringe has an open front end with an internally screw-threaded metal cap which is screw fitted onto external screw threads on the syringe. The cap has a boss for attachment of a needle assembly. Its circumference is knurled for improving manual gripping. It is a permanent part of the syringe unit and is not disposable.
U.S. Pat. No. 4,740,205 Seltzer et al describes a disposable needle system for receiving/dispensing fluids such as body fluids, medicaments, vaccines and the like. The needle is provided with a threaded plastic hub which is designed to be screwed into an aperture in the front wall of a tube holder. The tube holder is adapted to receive and support a tube or container for fluid. A sleeve rotatably mounted on the forward end of the tube holder comprises a socket-wrench-like device for rotating the needle hub to release the needle from the tube holder after use without requiring any human contact with the needle itself. A disc portion of the needle hub, which has an outer diameter greater than that of any other portion of the hub, is provided with radially outwardly extending drive arm elements for engagement with the wrench-like sleeve.
The drive arm elements fit into longitudinally extending drive slots formed in the front end of the socket wall. The sleeve does not have any internal configuration for engaging the needle hub. The drive arm elements on the disc portion of the hub do not fit inside the sleeve.
The system of Seltzer et al is not designed for use with a syringe. The wrench-like sleeve would be particularly awkward to accommodate on a dental syringe. Seltzer makes no provision for disengaging the rear point of the needle from the diaphragm of a cartridge of anaesthetic or the like. Due to frictional contact between the needle and the diaphragm, the needle would not be free to drop away from the tube holder after unscrewing of the hub, as described by Seltzer at column 7 lines 1-3 and lines 45-48. Allowing a used needle to drop downwardly into an awaiting receptacle involves a risk that the needle will fall outside the receptacle and may then have to be handled manually.
It is an object of the present invention to improve the needle/syringe assemblies which are commercially available and to provide a new and inventive disposal device.